Heart function can be significantly impaired when a heart valve is not functioning properly. Potential causes for heart valve malfunction include dilation of an annulus around the valve, ventricular dilation, and a prolapsed or misshapen valve leaflet. When the heart valve is unable to close properly, blood within a heart chamber can leak backwards, which is commonly referred to as regurgitation, through the valve. A defective heart valve may be treated by replacing the diseased valve with a replacement heart valve.
Artificial heart valves made from synthetic materials provide an attractive alternative to prosthetic heart valves. Prosthetic heart valves are constructed of animal tissues, such as bovine pericardium and porcine tissue, which are not durable as some available synthetic materials. Artificial heart valves made of synthetic materials can therefore function over a longer use life as compared to prosthetic heart valves. There are some limitations to using synthetic materials, however, as these materials are more prone to calcification. Heart valve calcification is a condition in which calcium deposits form on the leaflets of a heart valve and cause issues such as valve stenosis, blood flow restriction and possibly valve malfunction.
Differences in polymer structure and surface chemistry among some commonly available polymers, such as polyether urethanes and polycarbonate urethanes, may contribute to synthetic material calcification. New generation polyurethanes with siloxane soft segments have shown better performance but also have limitations. Even thermoplastic elastomers with polyisobutylene midblocks have not been without issues. Other studies have shown that surface modifications can mitigate the degree to which surfaces can become calcified. For example, approaches employing controlled release of bisphosphonates and surface modification using bisphosphonates, sulfate modifications, and glycoseaminoglycans such as hyaluronic acid and heparin, have been employed and evaluated. All these materials and approaches, however, have their limitations in effectiveness and manufacturability. There remains a continuing need for synthetic materials that minimize or prevent calcification such that a prosthetic heart valve can retain functionality throughout the life of a patient.